Sunday, August 28, 2005

Black levels - the achilles heel of digital video

DV and DVD Black Levels Part 2

Computer displays are cursed by fights over "gamma". Digital photography suffers from battles and confusion about embedded color profiles. Not surprisingly, digital video has its own achilles heel:
/// The analog inputs of North America NTSC TV's, VCR's and other equipment are designed for a black level of '7.5 IRE' (the 7.5 number is a reference point on a measurement scale for analog video). You may also hear this 7.5 IRE standard referred to as 'pedestal' or 'setup.' If you're in the rest of the world, using PAL equipment or the Japan NTSC standard, your equipment is designed for 0 IRE analog. We do it differently in North America because back in the Jurassic Age of television this 7.5 IRE black level was needed to make TV's work correctly. The rest of the world came up with a less-complicated way to do it.

The problem for DV users in North America is that DV 25 video equipment (named for the 25 megabit per second data rate of this popular video format), whether it is PAL or NTSC has an analog output of 0 IRE. In other words, your DV equipment uses the Japan NTSC standard and if you plug your DV gear into a video monitor or TV designed and calibrated for the North America NTSC system, the black level or levels you see will be wrong.

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